1. Field of the Invention
This invention relates to video image converters. More specifically, this invention relates to video image converters which operate in real time, such as at the rate of reception of an image in an input video image format (such as an input television video image signal), and to a component filter circuit for interpolating points in a horizontal and a vertical direction in the image.
2. Description of Related Art
Some advantages which may be obtained from converting video images from a one image format to another are disclosed in a related application titled "DIGITAL VIDEO IMAGE CONVERTER", now issued as U.S. Pat. No. 4,816,898. It is also advantageous to be able to convert images in real time. As used herein, converting images in "real time" means that as an input image is received, it is converted to an output image about as quickly as it is received, or at the least, that output image frames are generated quickly enough that a viewer does not notice a great deal of jerkiness. There are many advantages and applications of real-time conversion which are well known in the art.
One problem in the art is that real-time conversion of video images from one image format to another requires a great deal of computing power and memory storage, and may be impractical in its most general form. Moreover, the most general form of this computation is not thought to be easily approached by parallel computing techniques.
One known solution to this problem is to convert images by directing a video camera at a high-resolution monitor. While this method does alter the resolution in real time, but it has problems with linearity (i.e., it has a tendency to reproduce straight lines improperly) and it has a tendency to introduce aliasing (e.g., moire patterns or beat frequencies), both spatially (i.e., in the image) and temporally (i.e., flicker).
A second known solution is to just delete half (or some other fraction) of the input scan lines, and half the pixels in each scan line, typically by digital means. An enhancement of this technique is to delete pixels pseudo-randomly until only a correct number remain. While this method does alter resolution in real time, it is subject to problems produced by just deleting information, such as spatial aliasing. Also, small image features, such as thin lines, may be entirely lost.
A third known solution is to average successive pairs (or some other number, such as triplets) of lines to arrive at a lower-resolution image. However, this method is generally restricted to a fixed conversion ratio, such as 2:1 or 3:1, often requiring that portions of the image must be discarded to fit onto a standard monitor or within a standard television signal.
Another problem in the art is that known methods of real-time image conversion are narrowly tailored for a particular image format or a narrow range of image formats. This may make it difficult or impossible to operate such devices with other image formats. Even if it is possible to operate such devices with differing image formats, it may be difficult or impossible to quickly adjust such a device to change its image format. For example, known methods of real-time image conversion typically rely heavily on hardware devices whose conversion parameters are effectively fixed, either by the nature of their design or by the nature of the conversion method they use.
Accordingly, there is a need for video image converters (1) which can perform conversion of images from a source image format to a target image format in real time; and (2) which can perform conversion of images for a wide range of image formats and which can be adjusted to perform conversion of images for new image formats by reprogramming of software elements. There is a substantial advantage to be obtained from components of a video image converter which may perform data filtering in a horizontal and a vertical direction for the image at high speed and with a substantial degree of parallelism.